Control system for electrophotographic reproduction machines

ABSTRACT

A control system for electrophotographic reproduction machines including a control device responsive to increased current between corona charging wires and a surrounding screen caused by the introduction of a foreign body in proximity to the corona charging wires, the control device operating peripheral equipment in the electrophotographic reproduction machines.

United States Patent 11 1 Weber 1 1 CONTROL SYSTEM FOR ELECTROPHOTOGRAPI-HC REPRODUCTION MACHINES [76] Inventor: Guy Paul Weber, 25 Rue Verdier Monetti, 76 Arques La Bataille, France [22] Filed: Feb. 28, 1972 [211 App]. No.: 229,934

. [30] Foreign Application Priority Data Mar. 15, 1971 France .7108886 [52] US. Cl. .317/148.5 B, 250/495 ZC, 317/262 A, 317/D1G. 2 [51] Int. Cl. ..I'I01h 47/32 [58] Field of Search ..317/33 SC, 262A, 317/1485 B, DIG. 2, DIG. 8, DIG. 1; 250/4956 C, 49.5 ZC

SOURCE [451 Apr. 10, 1973 [56] References Cited UNITED STATES PATENTS 3,339,125 8/1967 Almy ..317/DIG. 2 3,493,791 2/ 1970 Adelson et a1 ..3 l7/DIG. 2

Primary Examiner-William M. Shoop, Jr. Assistant Examiner-Harry E. Moose, Jr.

7 Attorney-Leonard W. Sherman et a1.

[57] ABSTRACT 10 Claims, 3 Drawing Figures PATENTEU APR 1 01975 SOURCE '2. 3G: 4G, "JCT 1 CONTROL SYSTEM FOR ELECTROPI'IOTOGRAPHIC REPRODUCTION MACHINES BACKGROUND OF THE INVENTION '1. Field of the Invention The present invention pertains to electrophotographic reproduction machines and, more particularly, to systems for such machines to control the operation thereof in response to charging of a sheet of copy paper.

2. Discussion of the Prior Art In order to increase the operative lifetime of many components of electrophotographic reproduction machines, it is desirable to energize or operate such components only for the period of time required in the reproduction cycle and not continuously. Accordingly, electrophotographic reproduction machines employing such components normally include control devices operating such components so that they are intermittently energized only for that specific time required to properly reproduce an original. In many electrophotographic reproduction machines, operation is commenced upon the sensing of the introduction of an original or copy sheet of paper into the machine, and the sensing of the introduction of such original or copy paper is utilized to energize the intermittently operated components, such as lamps, motors and the like.

In order to sense the introduction of paper into electrophotographic reproduction machines, microswitches are commonly utilized; however, such microswitches are inherently fragile, easily damaged and have a tendency to provide inaccurate timing due to incorrect or inprecise handling of paper to be introduced into the machine, such as stuffing such paper into the machine. Accordingly, microswitches do not provide sufficient reliability and long use, and it is leakage current of a first level passing from the corona charging wire to the screen when no sheet of material to be charged is in proximity thereto and having a variation in the leakage current when a sheet of material to be charged is in proximity thereto, and a control circuit for sensing the variation in leakage current and responsive thereto to control the operation of the component whereby the component is operated in timed relation with the positioning of the sheet of material to generally preferred to use photo-electric cells or similar elements to detect the passage of paper at a specific position within the machine without physically contacting the paper as is required with microswitches. Photoelectric cells and similar detector elements have been successfully utilized to sense the passage of paper in electrophotographic reproduction machines; however, systems utilizing such detectors require special light sources and supplementary electrical circuitry normally requiring stabilization in order not to provide inadvertent operation. Accordingly, systems utilizing photo-electric cells for the detection of paper tend to be relatively complex, expensive andcumbersome and, therefore, do not present an entirely satisfactory solution to the problem of providing intermittent control for an electrophotographic reproduction machine.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a control system for electrophotographic reproduction machines that overcomes the above disadvantages while being relatively simple in construction and operation and offering increased reliability.

The present invention is generally characterized in a control system for operating a component of an electrophotographic reproduction machine including a corona charging device with at least one corona charging wire and a screen partially surrounding the corona charging wire, the corona charging device having a be charged at the corona charging device.

Another object of the present invention is to provide a control system for an electrophotographic reproduction machine without utilizing photo-cells or microswitches to detect the movement of paper.

The present invention has a further object in that the movement of a sheet of paper through a corona charging electrode device is sensed to control the operation of other components of the machine, for example, the energization of high intensity illumination lamps for exposing the electrophotographic copy paper from the original.

Yet another object of the present invention is to control the operation of an electrophotographic reproduction machine by sensing the proximity of a foreign body, such as a sheet of copy paper, at a corona charging device.

A further object of the present invention is to provide a control system for an electrophotographic reproduction machine of the type including at least one corona charging wire partially surrounded by a grounded screen to energize a semiconductor switch in response to current variation sensed in response to movement of a foreign body in proximity to the corona charging wire.

Some of the advantages of the control system of the present invention over the prior art are that the control system detects movement of paper without physically contacting the paper, the control system has a reduced number of components and may be easily installed and reliability of accurate detection is increased.

Other objects and advantages of the present'invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a chematic diagram of a conventional corona charging device for use with electrophotographic reproduction machines.

FIG. 2 is a schematic diagram of another conventional corona charging device for use with an electrophotographic reproduction machine.

FIG. 3 is a schematic diagram of a control system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The control system for eleclropliouigru hie reproduction machines oi the present invention will he better understood with reference to FIGS. I and 2 which are simplified schematic diagrams of conventional corona charging systems for such electrophotographic reproduction machines.

In the corona charging system of FIG. 1, a corona charging electrode device is generally indicated at 10 and includes a corona charging wire 12 electrically connected to receive a high positive or negative potential from a terminal 14 of a current generator or source of electricity 1 6, the other terminal 18 of source 16 being grounded. A screen 20 partially surrounds corona charging wire 12 and is grounded at 22; and, as

.' is'conventional, the corona electrode device may have I more than one corona charging wire with the screen 20 partially surrounding all such wires. When a foreign body 24, such as a sheet of electrophotographic copy paper or other material to be charged is moved in proximity to corona device 10, a high potential, such as I 6,000v.,'is supplied to wire 12 in order to ionize the fers from the corona charging system of FIG. '1 primarily only in the addition of another corona charging electrode device positioned diametrically opposite the first corona electrode device. The corona-charging system of FIG. 2 includes a positive corona electrode device 26 disposed directly above a negative corona electrode tional existing 1 l0 or 220 AC in order to provide the high positive and negative potentials on terminals 42 and 44, respectively. The source 40'has a high impedance and maybe considered a current generator to supply the high voltages at terminals 42 and 44.

A capacitance Cl is formed between the positive and negative corona charging wires 30 and 36, and a leakage resistance R1 extends thereacross, as shown in phantom. A capacitance C2 exists between corona charging wires 30 and screen 32, and a capacitance C3 exists across corona charging wires 36 and screen 38. Leakage resistors R2 and R3 are similarly formed across corona charging wires 30 and 36 and screens 32 and 38, respectively.

When no foreign body, such as a sheet of electrophotographic copy paper, is positioned between the corona electrode devices 26 and 28, a relatively high current passes between corona charging wires 30 and 36, such current having for example an intensity of several milliamps. At this time resistance R1 is low with the high internal resistance of source causing the voltage drop. The leakage current passing between the corona charging wires 30 and 36 and the screens 32 and 38 through leakage resistances R2 and R3, respectively, is accordingly low at this time.

If a foreign body, such as a conductive body, an object made of plastic orthe like or, more specifically, a sheet of electrophotographic copy paper 47 as indicated in dashed lines in FIG. 2, is moved between corona electrode devices 26 and 28, the capacitance I C1 will vary to a great extentand resistance R1 between the corona charging wires will undergo a substantial increase. Accordingly, :the current passing between wires 30 and 36 will be substantially reduced thereby reducing the voltage drop at the source 40. Since the voltage applied to the corona electrode devices will substantially increase and since C2, C3 and R2, R3 will remain substantially uncharged, the leakage current between the corona charging wires and the screens will accordingly increase.

The control system according to the present invention is based on the utilization of the variation in current caused by the introduction of a sheet of copy I paper or other foreign body in proximity to a corona electrode device to trigger an electrical circuit for use in controlling operation of peripheral equipment or components of an electrophotographic reproduction machine, such as to energize the high intensitylamps thereof.

The control system of the present invention will be described with reference to FIG. 3 wherein apreferred embodiment of such control system is illustrated. The corona charging system of FIG. 3 is similar to that illustrated and described with respect to FIG. 2, and identical reference numbers are utilized to identify identical components. The primary difference between the corona charging system of FIG. 2 and that of FIG. 3is

that in the corona charging system of FIG. 3, screen 32 is not directly grounded but rather is connected to ground through a variable resistor 48. An AC source 49 is illustrated as supplying a power input to source or current generator 40 which rectifies andsteps up the voltage to supply the high positive and negative potentials on terminals 42 and 44, respectively.

The junction of the resistor 48 and screen 32 is connected to a gate electrode of a controlled rectifier 49 which has its cathode connected to ground such that the gate to cathode voltage corresponds to the voltage drop across resistor 48. An AC source 50 is connected across a primary winding 52 of a transformer 54 which has a secondary winding 56 connected at one terminal to ground and at the other terminal to one junction of the parallel combination of a relay winding 58- and a holding capacitor 60; the other junction of the parallel combination being connected to the anode of -controlled rectifier 49. Relay winding 58 controls contacts 60 and 62 which are adapted to be connected in series between a source of electricity for the electrophotographic reproduction machines and a component to. be

intermittently operated. The controlled rectifier 49 is illustrated and described hereinafter as an SCR or thyristor; however, it will be appreciated that any switching device, preferably of semiconductor construction, such as a transistor or other three or four terminal controlled devices may be utilized with the control system of the present invention.

In operation, the source 40 maintains a high negative potential on corona charging wires 36 and a high positive potential on corona charging wires 30 in the same manner as described with respect to the corona charging system of FIG. 2. When a foreign body, such as the sheet of copyv paper 47, is introduced between the corona electrode devices 26 and 28, as illustrated in and relay means and a source of electricity connected in series between said anode and cathode of said controlled rectifier whereby said controlled rectifier is triggered in response to said variation in leakage current to energize said relay means.

8. A control system for operating a component of an electrophotographic reproduction machine comprising corona charging means adapted to receive a sheet of material to be charged, said corona charging means including first and second corona electrode devices disposed in diametric opposition to receive the sheet of material to be charged and high impedance generator means supplying a high positive potential to said first corona electrode device and a high negative potential to said second corona electrode device, said corona charging means having a leakage current of a first level prior to receiving the sheet of material to be charged and having a leakage current increasing above said first level after the sheet of material is received between said first and second corona electrode devices; and control means for sensing said increase in leakage cludes at least one corona charging wire and a screen' partially surrounding said corona charging wire, said leakage current passing from said corona chargingwire to said screen of one of said first or second corona electrode devices, and said control means includes means for sensing said leakage current passing from said screen to a reference potential.

10. The control system as recited in claim 9 wherein said current sensing means includes resistance means connected between said screen and the reference potential to receive said leakage current, and switch means responsive to the voltage drop across said resistance means. 

1. A control system for operating a component of an electrophotographic reproduction machine comprising corona charging means adapted to receive a sheet of material to be charged, said corona charging means including at least one corona charging wire and a screen partially surrounding said corona charging wire and having a leakage current of a first level prior to receiving the sheet of material to be charged and having a leakage current varying from said first level after receiving the sheet of material, said leakage current passing from said corona charging wire to said screen; and control means for sensing said variation in leakage current and responsive to said variation in leakage current to control the operation of the component whereby the component is operated in timed relation with the receiving of the sheet of material to be charged at said corona charging means.
 2. The control system as recited in claim 1 wherein said control means includes resistance means connected with said screen to receive said leakage current, and switch means connected across said resistance means and actuated in response to the voltage thereacross.
 3. The control system as recited in claim 2 wherein said switch means includes a controlled rectifier having a gate and a cathode connected across said resistance means, said controlled rectifier being maintained nonconductive by the voltage across said resistance means when said leakage current is at said first level and said controlled rectifier being rendered conductive by the voltage across said resistance means in response to said increased leakage current.
 4. The control system as recited in claim 3 wherein said control means includes a relay winding for controlling the operation of the component, said relay winding being connected in series with the anode and cathode of said controlled rectifier.
 5. The control system as recited in claim 1 wherein said control means includes means for sensing said leakage current passing from said screen to a reference potential.
 6. The control system as recited in claim 5 wherein said current sensing means includes resistance means connected between said screen anD the reference potential to receive said leakage current and switch means responsive to the voltage drop across said resistance means.
 7. The control system as recited in claim 6 wherein said leakage current increases above said first level after said corona charging means receives the sheet of material, and said resistance means includes a variable resistor, said switch means includes a controlled rectifier having a gate connected with said screen, a cathode connected with the reference potential and an anode, and relay means and a source of electricity connected in series between said anode and cathode of said controlled rectifier whereby said controlled rectifier is triggered in response to said variation in leakage current to energize said relay means.
 8. A control system for operating a component of an electrophotographic reproduction machine comprising corona charging means adapted to receive a sheet of material to be charged, said corona charging means including first and second corona electrode devices disposed in diametric opposition to receive the sheet of material to be charged and high impedance generator means supplying a high positive potential to said first corona electrode device and a high negative potential to said second corona electrode device, said corona charging means having a leakage current of a first level prior to receiving the sheet of material to be charged and having a leakage current increasing above said first level after the sheet of material is received between said first and second corona electrode devices; and control means for sensing said increase in leakage current and responsive to said increase in leakage current to control the operation of the component whereby the component is operated in timed relation with the receiving of the sheet of material to be cahrged at said corona charging means.
 9. The control system as recited in claim 8 wherein said first and second corona electrode devices each includes at least one corona charging wire and a screen partially surrounding said corona charging wire, said leakage current passing from said corona charging wire to said screen of one of said first or second corona electrode devices, and said control means includes means for sensing said leakage current passing from said screen to a reference potential.
 10. The control system as recited in claim 9 wherein said current sensing means includes resistance means connected between said screen and the reference potential to receive said leakage current, and switch means responsive to the voltage drop across said resistance means. 